1. Field of the Invention
This invention relates to a circuit interrupter and more particularly to a self-extinguishing gas circuit interrupter utilizing the arc energy dissipating from the electric arc established between the separated contacts to highly pressurize the surrounding SF.sub.6 gas which is released toward the arc to extinguish it upon the decrease of the arc current.
2. Description of the Prior Art
In a circuit interrupter for interrupting a high voltage, it has recently been proposed to utilize a technique for effecting arc extinction by utilizing an arc extinguishing fluid such as SF.sub.6 gas. Circuit interrupters utilizing this technique include the servo-extinguishing type gas circuit interrupter in which a high pressure arc extinguishing gas is puffed to the arc from a pressure chamber formed by a cylinder and a piston operatively connected to one of a pair of separable contacts, and the self-extinguishing type gas circuit interrupter in which a high pressure arc extinguishing gas is blasted by utilizing the pressure-rising phenomenon due to the arc energy dissipated to the surrounding arc extinguishing gas.
A typical self-extinguishing gas circuit interrupter utilizes the arc energy dissipated from the electric arc itself to highly pressurize the arc extinguishing gas within a defined space of a predetermined volume. When the arc inner pressure rapidly decreases due to the decrease of the arc current, this high pressure gas is released to extinguish the electric arc with its diffusing and cooling function due to the flow of the arc extinguishing gas. For such a self-extinguishing type gas circuit interrupter, the presence of pressure in the gas is indispensable both for the direct type and indirect type circuit interrupters. Also it is very effective for improving the arc extinguishing capability of the interrupter to expell the excessively ionized hot gas from the arcing region by utilizing the released high pressure gas. Further improvement in the arc extinguishing capability may be expected when this expulsion is effected within a short period of time. This is apparent from the fact that the interrupting capability and the interrupting capacity of the circuit interrupter are proportional to the pressure of the arc extinguishing gas in a gas puffer-type circuit interrupter.
With the conventional circuit interrupter, as the interrupting current increases, the pressure within the pressure chamber increases and the arc extinction capability is also proportionally improved. However, the structural strength of the pressure chamber must be made accordingly stronger. Since the typical pressure chamber is formed of an insulating material having an arc resistant property and insufficient in mechanical strength, the over all size of the pressure chamber must be large enough to obtain a pressure chamber having enough structural strength, resulting in one of the causes impeding realization of a small-sized, large capacity circuit interrupter.
With a larger pressure chamber, if the arc current is small and the pressure raising action is small, the arc extinguishing capability of the arc extinguishing gas is insufficient, and the temperature rise of the arc extinguishing gas degrades the arc diffusing capability of the gas due to the decrease in density and cooling capability.